Motor core and motor using the same

ABSTRACT

A motor generating cogging torque has one-quarter the cycle of basic cogging torque and an extremely small absolute value. First, in order to reduce the cycle of the cogging torque to one-half the cycle of the basic cogging torque, a basic configuration of the core is determined by setting opening angles of its slots to an appropriate electrical angle ranging from 80° to 95° and from 20° to 35°. Next, to produce the above-mentioned effects, an angular displacement of one-quarter the cycle of the basic cogging torque is provided in the motor. Furthermore, polarizing the core with a skew angle equal to one-half or less the cycle of the basic cogging torque at the same time allows the cogging torque to be reduced effectively while decrease in efficiency is minimized.

FIELD OF THE INVENTION

[0001] The present invention relates to a motor to be used forinformation, audiovisual, industrial equipment, and the like.

BACKGROUND OF THE INVENTION

[0002] Recently, higher-density recording is being promoted in themotors used for information, audiovisual equipment, etc. as representedby a digital video disk drive (DVD) unit and a hard disk drive (HDD)unit. With these advances, the motors used for such equipment arerequired to have higher rotational accuracy. There is also a growingdemand for motors used in the machinery for manufacturing such equipmentto have rotation accuracy high enough to meet the rotational accuracy ofthe equipment.

[0003] The causes of deteriorating the rotational accuracy of a motorare: (1) cogging torque resulting from a change in magnetic attractionforce between the core and the magnet of a motor; (2) torque ripplesproduced from the current flowing; and (3) irregular vibration resultingfrom the shaft whiling with some deviation in the bearing. Among thesecauses, this invention particularly addresses reduction of coggingtorque.

[0004] Conventional techniques of reducing cogging torque byspecifically designing plane configurations of cores are disclosed inJapanese Patent Application Non-examined Publication No.H04-304151,Japanese Patent Application Non-examined Publication No.H09-163649,Japanese Patent Application Non-examined Publication No.H09-285047, andothers.

[0005] The motor structure described in the above-mentioned JapanesePatent Application Non-examined Publication No.H04-304151 is shown inFIG. 52. In FIG. 52, the core reduces cogging torque by providing apositional relation with slightly different angles between salient poletips 311, 312, 321, 322, 331, 332 and respective poles of magnet 302.

[0006] Meanwhile, techniques of reducing cogging torque by changingaxial configurations instead of plane configurations of cores aredisclosed in Japanese Patent Application Non-examined PublicationNo.H02-254954 and Japanese Patent Application Non-examined PublicationNo.H03-3622.

[0007] The motor structure described in the above-mentioned JapanesePatent Application Non-examined Publication No.H02-254954 is shown inFIG. 53.

[0008] In FIG. 53, cylindrical core 401 is divided into upper core 411and lower core 412. The positional relation between upper core 411 andthe magnet is different from that between lower core 412 and the magnet.This structure cancels out the cogging torque waveforms generated by theupper and lower cores each other, thereby reducing the cogging torque ofthe entire motor.

[0009]FIG. 54 shows the structure of a motor armature described inJapanese Patent Application Non-examined Publication No.H03-3622.

[0010] In FIG. 54, laminated core 501 is configured by axiallylaminating cores in which salient poles have different opening angles(an angle a salient pole tip forms with respect to the center of thecore), or the salient poles of teeth have different widths at X and YThis structure allows different cogging torque waveforms to be canceled,thereby reducing cogging torque.

[0011] Techniques of reducing cogging torque using specifically designedmagnet polarization instead of core shapes are disclosed in JapanesePatent Publication No.2588661. A structure of a brushless motordescribed in the publication is shown FIG. 55.

[0012] In FIG. 55, the motor is made in 4:3 structure in whichring-shaped magnet 602 has 4 n poles and the stator core has 3 n poles.Skew angle θ2 of the magnetic poles of rotor magnet 602 is set as(30°/n)×0.8≦θ2≦(30°/n)×1.2. This structure reduces cogging torque anddistortion ratio of induced voltages.

[0013] However, these conventional techniques have the followingproblems.

[0014] First, among the techniques mentioned above, those utilizing coreshapes have not completely eliminated cogging torque even thoughproduced a certain extent of effects. Consequently, a level of coggingtorque remains producing at one-half the cycle of basic cogging torquedetermined by a least common multiple of the number of core slots andthe number of field poles.

[0015] Basic cogging torque may be calculated, for example, bydetermining the least common multiple (LCM) of the number of magneticpoles and the number of core slots in the motor. The LCM is divided into360 degrees to calculate a basic cogging torque cycle. For 8 poles and 6slots, for example, the basic cogging torque cycle is 15 degrees ((360degrees/LCM 24)=15 degrees).

[0016] Meanwhile, for conventional techniques of providing a magnet witha skew, a large skew angle is needed for effective reduction of coggingtorque. This generates more ineffective magnetic flux; thus involvingsuch adverse effects in performance as decreasing motor efficiency andincreasing core loss. Furthermore, as considerably affecting accuracy inpolarization or motor assembling, the conventional techniques have posedproblems such as unstable motor characteristics.

SUMMARY OF THE INVENTION

[0017] The present invention reduces the cycle of the cogging torqueproduced due to a basic configuration of a core to one-quarter or lessof the cycle of basic cogging torque determined by a least commonmultiple of the number of core salient poles and the number of fieldpoles, and to minimize the absolute value of the cogging torque as well.

[0018] The motor core of the present invention has the followingstructure.

[0019] A core used in a motor having magnetic field generating meanshaving N and S magnetic poles for generating a magnetic field and thecore made of magnetic material and opposed to the magnetic fieldgenerating means, where one of the magnetic field generating means andthe core rotates with respect to the other:

[0020] in which the number of magnetic poles is 2 m and the number ofcore slots is 6 n (m and n are integers), and

[0021] in which a basic configuration of the core is determined bysetting its slot opening angles (where “slot opening angle ” is an angleα slot opening forms with respect to the center of the core) to a valueranging from 80° to 95° in electrical angle α (each corresponding to(a/m)° in mechanical angle) and from 20° to 35° in electrical angleβ(each corresponding to (β/m)° in mechanical angle). This configurationallows the cycle of produced cogging torque to be reduced to one-halfthe cycle of basic cogging torque.

[0022] Electrical angle is defined in relationship to that portion ofthe core occupied by a pair of N and S magnets. One N and S magnet pairare assumed to occupy an electrical angle of 360 degrees. Thus, forexample, if a slot occupies one half of the circumference occupied by anN and S magnet pair, then the slot is said to have an electrical angleof 180 degrees.

[0023] In addition, two core shapes are combined so that the slots ineach core are displaced by an angle equal to one-quarter the cycle ofthe basic cogging torque ((90/k)° in mechanical angle [k is a leastmultiple of 2 m and 6 n]). This cancels different cogging torquewaveforms in the same motor, thereby reducing the resultant coggingtorque cycle to one-quarter the cycle of the basic cogging torque andalso minimizing the absolute value of the cogging torque.

[0024] Moreover, by polarizing the core with a skew angle equal toone-half or less the angle used for conventional techniques, the coggingtorque can be further reduced while decrease in motor efficiency isminimized.

BRIEF DESCRIPTION OF THE DRAWINGS

[0025]FIG. 1A shows a relation between a core slot opening angle (15°)and a magnet in accordance with a first embodiment of the presentinvention;

[0026]FIG. 1B shows a relation between a core slot opening angle (22.5°)and a magnet in accordance with the same embodiment;

[0027]FIG. 1C shows a relation between a core slot opening angle (30°)and a magnet in accordance with the same embodiment;

[0028] FIGS. 1D-F show relations between core slot opening angles and amagnet in accordance with the same embodiment

[0029]FIG. 2A shows a cogging torque waveform of the motor shown in FIG.1A;

[0030]FIG. 2B shows a cogging torque waveform of the motor shown in FIG.1B;

[0031]FIG. 2C shows a cogging torque waveform of the motor shown in FIG.1C;

[0032] FIGS. 2D-F show cogging torque waveforms of the motors shown inFIGS. 1D-1F.

[0033]FIG. 3 illustrates a relation between a magnet and a core slot ofthe motor shown FIG. 1B;

[0034]FIGS. 4A, 4B, 4C, and 4D illustrate reduction of cogging torque inthe motor shown in FIG. 13B;

[0035]FIGS. 5A, 5B, and 5C show examples of core shapes in accordancewith the same embodiment;

[0036]FIG. 6A shows a core shape in accordance with a second embodimentof the present invention;

[0037]FIG. 6B illustrates a core section displaced counterclockwise froma basic configuration in the core shape shown in FIG. 6A;

[0038]FIG. 6C illustrates a core section displaced clockwise from thebasic configuration in the core shape shown in FIG. 6A;

[0039]FIG. 7A shows a cogging torque waveform generated by the coreshape shown in FIG. 6B;

[0040]FIG. 7B shows a cogging torque waveform generated by the coreshape shown in FIG. 6C;

[0041]FIG. 7C shows a cogging torque waveform generated by the coreshape shown in FIG. 6A that is a combination of those shown in FIGS. 7Aand 7B;

[0042]FIG. 8A shows a core shape in accordance with a third embodimentof the present invention;

[0043]FIG. 8B illustrates a core section displaced counterclockwise froma basic configuration in the core shape shown in FIG. 8A;

[0044]FIG. 8C illustrates a core section displaced clockwise from thebasic configuration in the core shape shown in FIG. 8A;

[0045]FIG. 9A shows a core shape in accordance with a fourth embodimentof the present invention;

[0046]FIG. 9B illustrates a core section displaced counterclockwise froma basic configuration in the core shape shown in FIG. 9A;

[0047]FIG. 9C illustrates a core section displaced clockwise from thebasic configuration in the core shape shown in FIG. 9A;

[0048]FIG. 10A shows a core shape in accordance with a fifth embodimentof the present invention;

[0049]FIG. 10B illustrates a core section displaced counterclockwisefrom a basic configuration in the core shape shown in FIG. 10A;

[0050]FIG. 10C illustrates a core section displaced clockwise from thebasic configuration in the core shape shown in FIG. 10A;

[0051]FIG. 11A shows a core shape in accordance with a sixth embodimentof the present invention;

[0052]FIG. 11B illustrates a core section displaced counterclockwisefrom a basic configuration in the core shape shown in FIG. 11A;

[0053]FIG. 11C illustrates a core section displaced clockwise from thebasic configuration in the core shape shown in FIG. 11A;

[0054]FIG. 12A shows a core shape in accordance with a seventhembodiment of the present invention;

[0055]FIG. 12B illustrates a core section displaced counterclockwisefrom a basic configuration in the core shape shown in FIG. 12A;

[0056]FIG. 12C illustrates a core section displaced clockwise from thebasic configuration in the core shape shown in FIG. 12A;

[0057]FIG. 13A shows a core shape in accordance with an eighthembodiment of the present invention;

[0058]FIG. 13B illustrates a core section displaced counterclockwisefrom a basic configuration in the core shape shown in FIG. 13A;

[0059]FIG. 13C illustrates a core section displaced clockwise from thebasic configuration in the core shape shown in FIG. 13A;

[0060]FIG. 14A shows another core shape in accordance with the eighthembodiment of the present invention;

[0061]FIG. 14B illustrates a core section displaced counterclockwisefrom a basic configuration in the core shape shown in FIG. 14A;

[0062]FIG. 14C illustrates a core section displaced clockwise from thebasic configuration in the core shape shown in FIG. 14A;

[0063]FIG. 15A shows still another core shape in accordance with theeighth embodiment of the present invention;

[0064]FIG. 15B illustrates a core section displaced counterclockwisefrom a basic configuration in the core shape shown in FIG. 15A;

[0065]FIG. 15C illustrates a core section displaced clockwise from thebasic configuration in the core shape shown in FIG. 15A;

[0066]FIG. 16A shows still another core shape in accordance with theeighth embodiment of the present invention;

[0067]FIG. 16B illustrates a core section displaced counterclockwisefrom a basic configuration in the core shape shown in FIG. 16A;

[0068]FIG. 16C illustrates a core section displaced clockwise from thebasic configuration in the core shape shown in FIG. 16A;

[0069]FIG. 17A shows still another core shape in accordance with theeighth embodiment of the present invention;

[0070]FIG. 17B illustrates a core section displaced counterclockwisefrom a basic configuration in the core shape shown in FIG. 17A;

[0071]FIG. 17C illustrates a core section displaced clockwise from thebasic configuration in the core shape shown in FIG. 17A;

[0072]FIG. 18A shows still another core shape in accordance with theeighth embodiment of the present invention;

[0073]FIG. 18B illustrates a core section displaced counterclockwisefrom a basic configuration in the core shape shown in FIG. 18A;

[0074]FIG. 18C illustrates a core section displaced clockwise from thebasic configuration in the core shape shown in FIG. 18A;

[0075]FIG. 19A shows still another core shape in accordance with theeighth embodiment of the present invention;

[0076]FIG. 19B illustrates a core section displaced counterclockwisefrom a basic configuration in the core shape shown in FIG. 19A;

[0077]FIG. 19C illustrates a core section displaced clockwise from thebasic configuration in the core shape shown in FIG. 19A;

[0078]FIG. 20A shows still another core shape in accordance with theeighth embodiment of the present invention;

[0079]FIG. 20B illustrates a core section displaced counterclockwisefrom a basic configuration in the core shape shown in FIG. 20A;

[0080]FIG. 20C illustrates a core section displaced clockwise from thebasic configuration in the core shape shown in FIG. 20A;

[0081]FIG. 21A shows still another core shape in accordance with theeighth embodiment of the present invention;

[0082]FIG. 21B illustrates a core section displaced counterclockwisefrom a basic configuration in the core shape shown in FIG. 21A;

[0083]FIG. 21C illustrates a core section displaced clockwise from thebasic configuration in the core shape shown in FIG. 21A;

[0084]FIG. 22A shows still another core shape in accordance with theeighth embodiment of the present invention;

[0085]FIG. 22B illustrates a core section displaced counterclockwisefrom a basic configuration in the core shape shown in FIG. 22A;

[0086]FIG. 22C illustrates a core section displaced clockwise from thebasic configuration in the core shape shown in FIG. 22A;

[0087]FIG. 23A shows a core shape in accordance with a ninth embodimentof the present invention;

[0088]FIG. 23B illustrates a core section displaced counterclockwisefrom a basic configuration in the core shape shown in FIG. 23A;

[0089]FIG. 23C illustrates a core section of the basic configuration inthe core shape shown in FIG. 23A;

[0090]FIG. 23D illustrates a core section displaced clockwise from thebasic configuration in the core shape shown in FIG. 23A;

[0091]FIG. 24A shows another core shape in accordance with the ninthembodiment of the present invention;

[0092]FIG. 24B illustrates a core section displaced counterclockwisefrom a basic configuration in the core shape shown in FIG. 24A;

[0093]FIG. 24C illustrates a core section of the basic configuration inthe core shape shown in FIG. 24A;

[0094]FIG. 24D illustrates a core section displaced clockwise from thebasic configuration in the core shape shown in FIG. 24A;

[0095]FIG. 25A shows still another core shape in accordance with theninth embodiment of the present invention;

[0096]FIG. 25B illustrates a core section displaced counterclockwisefrom a basic configuration in the core shape shown in FIG. 25A;

[0097]FIG. 25C illustrates a core section of the basic configuration inthe core shape shown in FIG. 25A;

[0098]FIG. 25D illustrates a core section displaced clockwise from thebasic configuration in the core shape shown in FIG. 25A;

[0099]FIG. 26A shows still another core shape in accordance with theninth embodiment of the present invention;

[0100]FIG. 26B illustrates a core section displaced counterclockwisefrom a basic configuration in the core shape shown in FIG. 26A;

[0101]FIG. 26C illustrates a core section of the basic configuration inthe core shape shown in FIG. 26A;

[0102]FIG. 26D illustrates a core section displaced clockwise from thebasic configuration in the core shape shown in FIG. 26A;

[0103]FIG. 27A shows still another core shape in accordance with theninth embodiment of the present invention;

[0104]FIG. 27B illustrates a core section displaced counterclockwisefrom a basic configuration in the core shape shown in FIG. 27A;

[0105]FIG. 27C illustrates a core section of the basic configuration inthe core shape shown in FIG. 27A;

[0106]FIG. 27D illustrates a core section displaced clockwise from thebasic configuration in the core shape shown in FIG. 27A;

[0107]FIG. 28A shows still another core shape in accordance with theninth embodiment of the present invention;

[0108]FIG. 28B illustrates a core section displaced counterclockwisefrom a basic configuration in the core shape shown in FIG. 28A;

[0109]FIG. 28C illustrates a core section of the basic configuration inthe core shape shown in FIG. 28A;

[0110]FIG. 28D illustrates a core section displaced clockwise from thebasic configuration in the core shape shown in FIG. 28A;

[0111]FIG. 29A shows a core shape in accordance with a tenth embodimentof the present invention;

[0112]FIGS. 29B, 29C, 29D, and 29E illustrate core sections 90° inelectrical angle out of phase each other constituting the core shapeshown in FIG. 29A;

[0113]FIG. 30A shows another core shape in accordance with the tenthembodiment of the present invention;

[0114]FIGS. 30B, 30C, 30D, and 30E illustrate core sections 90° inelectrical angle out of phase each other constituting the core shapeshown in FIG. 30A;

[0115]FIG. 31A illustrates a vertical section of a laminated core shapein accordance with an eleventh embodiment of the present invention;

[0116]FIG. 31B illustrates a cross section taken on line 31B-31B of thecore shape shown in FIG. 31A;

[0117]FIG. 31C illustrates a cross section taken on line 31C-31C of thecore shape shown in FIG. 31A;

[0118]FIG. 32A shows a cogging torque waveform of the core shape shownin FIG. 31B;

[0119]FIG. 32B shows a cogging torque waveform of the core shape shownin FIG. 31C;

[0120]FIG. 32C shows a cogging torque waveform generated by the coreshape shown in FIG. 31A that is a combination of those shown in FIGS.32A and 32B;

[0121]FIG. 33A illustrates a vertical section of a laminated core shapein accordance with a twelfth embodiment of the present invention;

[0122]FIG. 33B illustrates a cross section taken on line 33B-33B of thecore shape shown in FIG. 33A;

[0123]FIG. 33C illustrates a cross section taken on line 33C-33C of thecore shape shown in FIG. 33A;

[0124]FIGS. 34A and 34B illustrate the configuration of core sectionsconstituting the core shape shown in FIG. 33A;

[0125]FIG. 35A illustrates a vertical section of a laminated core shapein accordance with a thirteenth embodiment of the present invention;

[0126]FIG. 35B illustrates a cross section taken on line 35B-35B of thecore shape shown in FIG. 35A;

[0127]FIG. 35C illustrates a cross section taken on line 35C-35C of thecore shape shown in FIG. 35A;

[0128]FIGS. 36A and 36B illustrate the configuration of core sectionsconstituting the core shape shown in FIG. 35A;

[0129]FIG. 37A illustrates a vertical section of a laminated core shapein accordance with a fourteenth embodiment of the present invention;

[0130]FIG. 37B illustrates a cross section taken on line 37B-37B of thecore shape shown in FIG. 37A;

[0131]FIG. 37C illustrates a cross section taken on line 37C-37C of thecore shape shown in FIG. 37A;

[0132]FIGS. 38A and 38B illustrate the configuration of core sectionsconstituting the core shape shown in FIG. 37A;

[0133]FIG. 39A illustrates a vertical section of a laminated core shapein accordance with a fifteenth embodiment of the present invention;

[0134]FIG. 39B illustrates a cross section taken on line 39B-39B of thecore shape shown in FIG. 39A;

[0135]FIG. 39C illustrates a cross section taken on line 39C-39C of thecore shape shown in FIG. 39A;

[0136]FIGS. 40A and 40B illustrate the configuration of core sectionsconstituting the core shape shown in FIG. 39A;

[0137]FIG. 41A illustrates a vertical section of a laminated core shapein accordance with a sixteenth embodiment of the present invention;

[0138]FIG. 41B illustrates a cross section taken on line 41B-41B of thecore shape shown in FIG. 41A;

[0139]FIG. 41C illustrates a cross section taken on line 41C-41C of thecore shape shown in FIG. 41A;

[0140]FIGS. 42A and 42B illustrate the configuration of core sectionsconstituting the core shape shown in FIG. 41A;

[0141]FIG. 43A shows a cross-sectional view of a salient-pole windingpart of a core in accordance with the sixteenth embodiment of thepresent invention;

[0142]FIG. 43B shows a cross-sectional view of a salient-pole windingpart of a core having a constant width of the present invention;

[0143]FIGS. 44A and 44B illustrate core parts in accordance with aseventeenth embodiment of the present invention;

[0144]FIG. 45A illustrates a vertical section of a laminated core shapein accordance with an eighteenth embodiment of the present invention;

[0145]FIG. 45B illustrates a cross section taken on line 45B-45B of thecore shape shown in FIG. 45A;

[0146]FIG. 45C illustrates a cross section taken on line 45C-45C of thecore shape shown in FIG. 45A;

[0147]FIG. 45D illustrates a cross section taken on line 45D-45D of thecore shape shown in FIG. 45A;

[0148]FIG. 45E illustrates a cross section taken on line 45E-45E of thecore shape shown in FIG. 45A;

[0149]FIG. 46A illustrates a vertical section of a laminated core shapein accordance with a nineteenth embodiment of the present invention;

[0150]FIG. 46B illustrates a cross section taken on line 46B-46B of thecore shape shown in FIG. 46A;

[0151]FIG. 46C illustrates a cross section taken on line 46C-46C of thecore shape shown in FIG. 46A;

[0152]FIGS. 47A and 47B partially illustrate the cross section of thecore shape taken on line 46B-46B as shown in FIG. 46B;

[0153]FIGS. 47C and 47D partially illustrate the cross section of thecore shape taken on line 46C-46C as shown FIG. 46C;

[0154]FIG. 48A shows another core shape in accordance with thenineteenth embodiment of the present invention;

[0155]FIG. 48B illustrates a cross section taken on line 48B-48B of thecore shape shown in FIG. 48A;

[0156]FIG. 48C illustrates a cross section taken on line 48C-48C of thecore shape shown in FIG. 48A;

[0157]FIGS. 49A and 49B partially illustrate the cross section of thecore shape taken on line 48B-48B as shown FIG. 48B;

[0158]FIGS. 49C and 49D partially illustrate the cross section of thecore shape taken on line 48C-48C as shown FIG. 48C;

[0159]FIG. 50 shows polarized condition of a magnet in accordance with atwentieth embodiment of the present invention;

[0160]FIG. 51A shows cogging torque-skew angle characteristics of thesame embodiment;

[0161]FIG. 1B shows efficiency-skew angle characteristics of he sameembodiment;

[0162]FIG. 52 shows a motor of a conventional technique described inJapanese Patent Application Non-examined Publication No. H04-304151;

[0163]FIG. 53 shows a motor core of a conventional technique describedin Japanese Patent Application Non-examined Publication No. H02-254954;

[0164]FIG. 54 shows a rotating armature of a rotating machine of aconventional technique described in Japanese Patent ApplicationNon-examined Publication No. H03-3622; and

[0165]FIG. 55 shows a motor of a conventional technique described inJapanese Patent Publication No. 2588661.

DETAILED DESCRIPTION OF THE INVENTION

[0166] Exemplary embodiments of the present invention will be describedhereinafter with reference to the accompanying drawings.

[0167] (First Embodiment)

[0168]FIGS. 1A, 1B, and 1C show relations between core 1 of a motor andmagnet 2 functioning as magnetic field generating means. Magnet 2 hasfour N poles and four S poles disposed alternately with an equal angularpitch. Core 1 has six slots 3 equally spaced each other.

[0169] A difference in FIGS. 1A, 1B, and 1C are only the angles theopenings of slots 3 provided in core 1 form with respect to the centerof the core (hereinafter referred to as a “slot opening angle ”). Theslot opening angles are set to become larger in steps: 15° in mechanicalangle (60° in electrical angle) for FIG. 1A; 22.5° in mechanical angle(90° in electrical angle) for FIG. 1B; and 30° in mechanical angle (120°in electrical angle) for FIG. 1C.

[0170] When magnet 2 rotates with respect to core 1, the force ofattraction between core 1 and magnet 2 periodically changes, whichgenerates torque ripples called “cogging torque” between core 1 andmagnet 2.

[0171]FIGS. 2A, 2B, and 2C show waveforms of cogging torque produced inthe motors shown FIGS. 1A, 1B, and 1C, respectively. The cogging torqueof the motor shown in FIG. 1A has a waveform repeated 24 times perrevolution as shown in FIG. 2A. This figure corresponds to the leastcommon multiple “24” of the number of core slots “6” and the number ofmagnet poles “8”. This is not limited to this motor, but it is commonfor ordinary motors to be subjected to such cogging torque, i.e. thecogging torque having a cycle equal to the least common multiple of thenumber of core slots and the number of magnet poles (this cycle ishereinafter referred to as a “cycle of basic cogging torque”).

[0172] For the motor shown in FIG. 1C, or in the case where the openingangles of slots 3 are large, as understood from comparison between FIGS.2A and 2C, the cycles and absolute values of the cogging torque aresubstantially equal but the waveforms are 180° out of phase. For themotor shown in FIG. 1B, or in the case where the opening angles of slots3 are set to 90° in electrical angle, as shown in FIG. 1B, coggingtorque having one-half the cycle of basic cogging torque, in otherwords, twice the frequency of the basic cogging torque is produced andits absolute value is reduced considerably.

[0173] The reasons for these phenomena will be described with referenceto FIGS. 3 and 4A to 4D. For ease of explanation, FIG. 3 shows acondition when the transition part between N and S poles of magnet 2 isapproaching edge 35 of core slot 3. Now, FIG. 4A shows how torque varieswith changes in rotation angles (indicated in electrical angle). Thatis, rotation of magnet 2 accompanies change in the magnetic energybetween magnet 2 and core 1, thus generating torque as shown in FIG. 4A.In this waveform, torque reaches zero when edge 35 of slot 3 almostmeets the pole transition part.

[0174] Likewise, at opposite edge 36 of slot 3, similar torque isgenerated. Also in this torque waveform, torque reaches zero when edge36 of slot 3 almost meets the pole transition part. The waveforms shownin FIGS. 4B and 4A are symmetric with respect to a point. Now, when theopening angles of slot 3 are set to 90° in electrical angle, the torquewaveforms generated at edges 35 and 36 opposing each other of slot 3 are180° out of phase, and whereby cancelled. As a result, within one slot3, the third-order components are eliminated to form a torque waveformas shown FIG. 4C. While this torque waveform is generated in one slot 3,the torque waveform generated in the entire motor is a synthesis of thetorque waveforms generated in all the slots. Therefore, in the motor asa whole, since the first-, second-, fourth-, fifth-, seventh-ordercomponents, etc. of the torque waveform shown in FIG. 4C are cancelledby the torque waveforms each 120° out of phase in electrical angle thatare generated in other five slots, torque of higher-than-sixth-ordercomponents appears as shown in FIG. 4D. Consequently, the entire motorgenerates cogging torque having a waveform repeated 48 times perrevolution (with one-half the cycle of the basic cogging torque) andminimized absolute value.

[0175] In this first embodiment, it has shown that cogging torque isminimized when the opening angles of slots are 90° in electrical angle.Similarly, when the opening angles of slots is 30°, torque waveforms 60°out of phase are also produced at both opposite edges of one slot; andtherefore, the third-order components of the cogging torque waveformsgenerated in the slot are eliminated and a phenomenon similar to theabove occurs.

[0176] In the first embodiment, it has shown that cogging torque isminimized when the opening angles of slots are 90°. As for other anglesaround 90°, the third-order components of the cogging torque produced inslot 3 are eliminated by 50% when the opening angles are set to 80° or100® in electrical angle. When the opening angles of slots are set to85° or 95° in electrical angle, the third-order components of thecogging torque produced in one slot are eliminated by 74%. For thesereasons, in order to attain practical performance, setting openingangles to a value ranging from 85° to 95°, at which the third-ordercomponents of the cogging torque waveforms generated in one slot areeliminated to about one quarter or less, allows the basic cyclecomponents of the cogging torque to be reduced considerably, thusminimizing the cogging torque.

[0177] When tips of salient poles 4 are shaped non-circular as shown inFIGS. 5A through 5C, or such effects as magnetic saturation of the coreare taken into account, the slots can be considered to have a largeopening angle from the viewpoint of magnetic properties. For thisreason, when the opening angle θ of slot 3 is relatively small (about 5°in electrical angle), cogging torque may be minimized.

[0178] Consequently, in general, when the slot opening angles are set toan appropriate value ranging from 85° to 95°, or 20° to 35°, coggingtorque having one-half the cycle of basic cogging torque is produced andits absolute value can be minimized, irrespective of the number ofmagnet poles and core slots.

[0179] Each of the following embodiments will show the techniques offurther reducing the cogging torque based on a basic core configurationthat inherently produces little cogging torque having one-half the cycleof basic cogging torque.

[0180] (Second Embodiment)

[0181]FIG. 6A shows a core shape in accordance with a second embodiment.In FIG. 6A, core 1 is configured so that the opening angles of salientpole tips are constant at 37.5° in mechanical angle (150° in electricalangle), and salient pole tips 41 on a half side of the core aredisplaced 1.875° (one-eighth the cycle of basic cogging torque)clockwise and salient pole tips 42 on the other half are displaced1.875° counterclockwise.

[0182] The shape of core 1 is based on the following ideas.

[0183] In FIG. 6B, core 5 is configured so that the opening angle ofslot 3 is set to 90° in electrical angle and salient pole tip 4 isdisplaced 1.875° (one-eighth the cycle of basic cogging torque)counterclockwise. This core 5 has salient pole tip 4 configured in amanner slightly different from a basic configuration; however, as shownby the solid line in FIG. 7A, the core produces cogging torque identicalto that produced by the basic configuration except that the phase isslightly different

[0184] In FIG. 6C, core 6 is configured so that the opening angle ofslot 3 is set to 90° in electrical angle and salient pole tip 4 isdisplaced 1.875° clockwise. Likewise, as shown by the solid line in FIG.7B, the core 6 also produces cogging torque identical to that producedby the basic configuration except that the phase is slightly different.

[0185] The cogging torque produced in these two cores 5 and 6 areidentical in absolute value but 180° out of phase (3.75° in mechanicalangle, one-quarter the cycle of the basic cogging torque).

[0186] Core 1 of the second embodiment (FIG. 6A) is configured bycombining the diagonally shaded parts of cores 5 and 6 shown in FIGS. 6Band 6C, respectively. The diagonally shaded parts and the other parts inFIG. 6B have equal positional relations with the magnet, so the coggingtorque produced by the shaded parts has one-half the absolute value ofthe cogging torque produced by the entire core and in phase with it. Thesame holds true for the core shape shown in FIG. 6C. For core 1 of thesecond embodiment (FIG. 6A) in which these two shapes are combined,cogging torque waveforms generated by the respective shapes cancel outeach other, thus canceling odd-numbered-order components of the coggingtorque waveforms. Therefore, as shown in FIG. 7C, resultant coggingtorque has a waveform repeated 96 times per revolution, and its cycle isone-half (one-quarter the cycle of the basic cogging torque) and itsabsolute value is less than one-half of those produced by the basicconfiguration.

[0187] The above-mentioned structure reduces a cycle of cogging torqueto one-quarter or less the cycle of ordinary cogging torque as well asits absolute value. Therefore, the cogging torque can be reduced to theextent that its cycle is one-half and its absolute value is less thanone-half of those produced with the conventional techniques described inJapanese Patent Application Non-examined Publication No. H04-304151, andothers.

[0188] (Third Embodiment)

[0189]FIG. 8A shows a core shape in accordance with a third embodiment.

[0190] In FIG. 8A, core 1 is configured so that the opening angles ofslots are constant at 90° in electrical angle, slots 31 on a half sideof the core are displaced 1.875° (one-eighth the basic cogging cycle)clockwise and slots 32 on the other half are displaced 1.875°counterclockwise.

[0191] Similar to the second embodiment mentioned above, this shape is acombination of the halves of cores 5 and 6 shown in FIGS. 8B and 8C thatgenerate cogging torque waveforms 180° out of phase. This shape hascompletely the same effects as those produced by the second embodiment.

[0192] (Fourth Embodiment)

[0193]FIG. 9A shows a core shape in accordance with a fourth embodiment.

[0194] In FIG. 9A, core 1 is configured so that slots are disposed withan equal angular pitch, and slots 31 each having an opening angle of18.75° (90° in electrical angle − one-quarter the cycle of basic coggingtorque) and slots 32 each having an opening angle of 26.25° (90° inelectrical angle + one-quarter the cycle of the basic cogging torque)are alternately provided. The configuration of this core 1 is similar tothose of the techniques described in Japanese Patent ApplicationNon-examined Publication No. H04-304151. However, in accordance with thepresent invention, the angular displacement of salient pole tip 4 isone-half of that described in the above-mentioned publication. The coreshape of this embodiment reduces cogging torque, making its absolutevalue less than one-half while maintaining the efficiency produced bythe basic configuration as much as possible.

[0195] (Fifth Embodiment)

[0196]FIG. 10A shows a core shape in accordance with a fifth embodiment.

[0197] In FIG. 10A, core 1 is configured so that salient pole tips aredisposed with an equal angular pitch, and salient poles tips 41 eachhaving an opening angle of 33.75° (150° in electrical angle −one-quarter the cycle of basic cogging torque) and salient pole tips 42each having an opening angle of 41.25° (150° in electrical angle +one-quarter the cycle of the basic cogging torque) are alternatelyprovided.

[0198] Since the core shapes described in these fourth and fifthembodiments are more laterally symmetrical than the shapes described inthe second and third embodiments, the shapes of fourth and fifthembodiments are less susceptible to directional influence when assembledand more advantageous for mass production. They are also moreadvantageous to improve rotational accuracy because of their excellentmagnetic balance in lateral direction.

[0199] (Six Embodiment)

[0200]FIG. 11A shows a core shape in accordance with a sixth embodiment.

[0201] In FIG. 1A, core 1 is configured so that salient pole tips aredisposed with an equal angular pitch, and salient pole tips 41 on a halfside of the core have an opening angle of 33.75° (150° in electricalangle − one-quarter the cycle of basic cogging torque) and salient poletips 42 on the other half have an opening angle of 41.25° (150° inelectrical angle + one-quarter the cycle of the basic cogging torque).

[0202] Contrary to the cases described in these fourth and fifthembodiments, this shape intends to unbalance lateral magnetic condition.This unbalanced condition adds force of always attracting the magnettoward one direction, thus providing an action for preventing the rotorfrom whirling with some deviation. This shape is advantageous to improverotational accuracy when slide bearings such as an oil impregnated metalpowder sintered bearing are used as the bearing.

[0203] (Seventh Embodiment)

[0204]FIG. 12A shows a core shape in accordance with a seventhembodiment.

[0205] In FIG. 12A, core 1 is configured so that slots are disposed withan equal angular pitch, and slots 31 on a half side of the core have anopening angle of 18.75° (90° in electrical angle − one-quarter the cycleof basic cogging torque) and slots 32 on the other half have an openingangle of 26.25° (90° in electrical angle + one-quarter the cycle of thebasic cogging torque). With intentionally unbalanced lateral magneticcondition, this shape also has the same effects that have been producedby the sixth embodiment.

[0206] Furthermore, in the core shape of the seventh embodiment, slots32 having a larger opening angle disposed on one side serve as suitablespaces for placing position sensitive elements such as Hall elements.

[0207] Like these, in these second through seventh embodiments, caseswhere the number of magnet poles is “8” and the number of core slots is“6” have been described as examples. The similar techniques areapplicable to motors having a different number of magnetic poles or coreslots.

[0208] (Eighth Embodiment)

[0209] In the eighth embodiment, cases where the same technique isapplied to motors having “16” magnet poles and “12” core slots will bedescribed.

[0210]FIG. 13A shows a core shape in accordance with the eighthembodiment. In this embodiment, since the number of magnet cores (notshown) is “16”, a mechanical angle of 45° corresponds to an electricalangle of 360°.

[0211] In FIG. 13A, core 1 is configured so that the opening angles ofsalient pole tips are constant at 150° in electrical angle (18.75° inmechanical angle), and salient pole tips 41 on a half side of the coreare displaced 0.9375° (one-eighth the cycle of basic cogging) clockwiseand salient pole tips 42 on the other half are displaced 0.9375°counterclockwise. For this configuration, the technique described in thesecond embodiment is employed, and its effects are the same as thoseproduced by the second embodiment.

[0212]FIGS. 14A through 18A show other core shapes in accordance withthe eighth embodiment.

[0213] In FIG. 14A, core 1 is configured so that the opening angles ofslots are constant at 90° in electrical angle (11.25° in mechanicalangle), and slots 31 on a half side of the core are displaced 0.9375°(one-eighth the cycle of basic cogging torque) clockwise and slots 32 onthe other half are displaced 0.9375° counterclockwise. For thisconfiguration, the technique described in the third embodiment isemployed, and its effects are the same as those produced by the thirdembodiment.

[0214] In FIG. 15A, core 1 is configured so that slots are disposed withan equal angular pitch, and slots 31 each having an opening angle of9.375° (90° in electrical angle − one-quarter the cycle of basic coggingtorque) and slots 32 each having an opening angle of 13.125° (90° inelectrical angle + one-quarter the cycle of the basic cogging torque)are alternately provided. For this configuration, the techniquedescribed in the fourth embodiment is employed, and its effects are thesame as those produced by the fourth embodiment.

[0215] In FIG. 16A, core 1 is configured so that salient pole tips aredisposed with an equal angular pitch, and salient poles tips 41 eachhaving an opening angle of 16.875° (150° in electrical angle −one-quarter the cycle of basic cogging torque) and salient poles tips 42each having an opening angle of 20.625° (150° in electrical angle +one-quarter the cycle of the basic cogging torque) are alternatelyprovided. For this configuration, the technique described in the fifthembodiment is employed, and its effects are the same as those producedby the fifth embodiment.

[0216] In FIG. 17A, core 1 is configured so that salient pole tips aredisposed with an equal angular pitch, and salient pole tips 41 on a halfside of the core have an opening angle of 16.875° (150° in electricalangle − one-quarter the cycle of basic cogging torque) and salient poletips 42 on the other half have an opening angle of 20.625° (150° inelectrical angle + one-quarter the cycle of the basic cogging torque).For this configuration, the technique described in the sixth embodimentis employed, and its effects are the same as those produced by the sixthembodiment.

[0217] In FIG. 18A, core 1 is configured so that slots are disposed withan equal angular pitch, and slots 31 on a half side of the core have anopening angle of 9.375° (90° in electrical angle − one-quarter the cycleof basic cogging torque) and slots 32 on the other half have an openingangle of 13.125° (90° in electrical angle + one-quarter the cycle of thebasic cogging torque). For this configuration, the technique describedin the seventh embodiment is employed, and its effects are the same asthose produced by the seventh embodiment.

[0218] In addition, FIGS. 19A through 22A also show still other coreshapes in accordance with the eighth embodiment.

[0219] When the number of the slots is “12”, two types of configurationscan be used. For one type, as shown in FIG. 19A or 20A, the openingangles of salient pole tips are constant at 18.75° (150° in electricalangle), and salient poles are disposed with different angular pitches.For the other type, as shown in FIG. 21A or 22A, the opening angles ofcore slots are constant at 11.25° (90° in electrical angle), and slotsare disposed-with different angular pitches.

[0220] These second through eighth embodiments are the examples designedaccording to basic configurations in which the opening angles of coreslots are set to 90° in electrical angle. As described in the firstembodiment, it is preferable to set the opening angles of core slots ofa basic configuration to an appropriate value ranging from 80° to 95°and 20° to 35°. For each of these embodiments in which slot openingangles are set to 90° in electrical angle and the number of magnet polesare set to 2 m (m is an integer), the preferable range of slot openingangles can be generalized as from (80/m)° to (90/m)° and from (20/m)° to(35/m)° in mechanical angle.

[0221] In addition, the above-mentioned preferable range can begeneralized for the opening angles of salient pole tips. When a ratio ofthe number of magnet poles to the number of core slots is 4:3, for acore in which the opening angles of its salient pole tips are set to150° in electrical angle, the preferable range of a salient pole tipopening angle can be generalized as from (145/m)° to (160/m)° and from(205/m)° to (220/m)° in mechanical angle in a similar manner.

[0222] Even in cases of different number of magnet poles or core slots,the above-mentioned preferable range can be used. When the number ofmagnet poles is 2 m and the number of core slots is 6 n (m and n areintegers), generally, a basic configuration of a core shape thatproduces cogging torque having one-half the cycle of basic coggingtorque is determined by setting its slot opening angles to anappropriate value ranging from 80° to 95° and from 20° to 35° inelectrical angle (from (80/m)° to (90/m)° and from (20/m)° to (35/m)° inmechanical angle). Furthermore, combining two core shapes each havingthe slots displaced by an angle equal to one-quarter the cycle of basiccogging torque ((90/k)° in mechanical angle [k is a least commonmultiple of 2 m and 6 n]) can provide a motor in which the coggingtorque has one-quarter the cycle of the basic cogging torque and itsabsolute value is considerably reduced.

[0223] (Ninth Embodiment)

[0224] The above second through eighth embodiments are cases where acore has a even number of slots; and even with a core having an oddnumber of slots, the same effects are produced as well in a mannerdescribed below.

[0225] In the ninth embodiment, a case where the number of magnet polesis “12” and the number of core slots is “9” will be described as anexample. Since the number of the magnet poles is “12”, a mechanicalangle of 60° corresponds to an electrical angle of 360°. The leastcommon multiple of “12” and “9” is “36”; and thus the cycle of basiccogging torque is 10° in mechanical angle, or 60° in electrical angle.

[0226] In these second through eighth embodiments, two core shapesgenerating cogging torque waveforms 180° out of phase (one-quarter thecycle of basic cogging torque) each other are combined. As for the ninthembodiment, a core is configured by combining three shapes generatingwaveforms 120° out of phase each other.

[0227]FIG. 23A shows a core shape in accordance with the ninthembodiment.

[0228] Core 7 of the ninth embodiment (FIG. 23A) is configured bycombining a third of core 9 of a basic configuration as shown in FIG.23C, a third of core 8 in which salient pole tips of the basicconfiguration are displaced 1.667° (one-sixth the cycle of the basiccogging torque) counterclockwise as shown in FIG. 23B, and a third ofcore 10 in which salient pole tips of the basic configuration aredisplaced 1.667° clockwise as shown in FIG. 23D The cogging torque wavesgenerated in core 8, 9, and 10 shown in FIGS. 23B, 23C, and 23D,respectively, are equal in absolute value and waveform, but 120° out ofphase each other. In the cogging torque waveform generated by core 7that is a combination of these core thirds, the first-, second-,fourth-, fifth-, seventh-order components, etc. are cancelled; and thusthe cycle of cogging torque is reduced to one-third of that generated bythe basic configuration and its absolute value is also reduced.According to the similar idea, core shapes shown in FIGS. 24A through28A can be produced as well.

[0229] In addition, even to cases of a different number of magnet polesor core slots, the above idea can be applied. When the number of magnetpoles is 2 n and the number of core slots is 3 n (m and n are integers),generally, a basic configuration of a core shape producing coggingtorque having one-half the cycle of basic cogging torque is determinedby setting its slot opening angles to an appropriate value ranging from80° to 95° and from 20° to 35° in electrical angle (from (80/m)° to(95/m)° and from (20/m)° to (35/m)° in mechanical angle). Furthermore,combining three core shapes each having the slots displaced by an angleequal to one-sixth the cycle of the basic cogging torque ((60/k)° inmechanical angle [k is a least common multiple of 2 m and 6 n]) allowsthe cycle of cogging torque to be reduced to one-half the cycle of thebasic cogging torque (an effect of the basic configuration)×⅓ (an effectof the combination of these three core shapes) i.e. one-sixth the cycleof the basic cogging torque, and its absolute value to be reducedconsiderably as well.

[0230] (Tenth Embodiment)

[0231] In these second through ninth embodiments, a combination of twoor three core shapes has produced cogging torque having one-quarter orone-sixth the cycle of basic cogging torque. As for the tenthembodiment, a technique of further reducing the cogging torque using acombination of four or more core shapes.

[0232] In the tenth embodiment, examples of combinations of four shapesgenerating cogging torque waveforms 90° out of phase each other will bedescribed.

[0233]FIG. 29A shows a core shape in accordance with the tenthembodiment. In the tenth embodiment, a case where the number of magnetpoles is “16” and the number of slots is “12” is described as anexample. Since the number of the magnet poles is “16”, a mechanicalangle of 45° corresponds to an electrical angle of 360°. The leastcommon multiple of “16” and “12” is “48”; and thus the cycle of basiccogging torque is 7.5° in mechanical angle, or 60° in electrical angle.

[0234] Core 11 of the tenth embodiment is configured by combiningfourths of four cores 12, 13, 14, and 15. As shown in FIGS. 29B through29E, in those cores, respective cogging torque waveforms are made 90°out of phase each other by providing the salient pole tips of eachfourth with angular displacement by 0.9375° (one-eighth the cycle of thebasic cogging torque) each.

[0235] In the cogging torque waveform generated by core 11 made of acombination of these fourths, the odd-numbered-order components andsecond-order components are cancelled out; and whereby its cycle is madeone-quarter the cycle of the basic cogging torque and its absolute valueis further reduced. According to the similar idea, a core shape shown inFIG. 30A and other various shapes can be produced. Thus, motors having aslightly complicated core shape but extremely minimized cogging torquecan be provided.

[0236] For the motors shown FIGS. 29A and 30A, the cycle of coggingtorque is reduced to one-half the cycle of basic cogging torque (aneffect of the basic configuration)×¼ (an effect of the combination ofthese four core shapes), i.e. one-eighth the cycle of the basic coggingtorque, and it absolute value is also reduced considerably.

[0237] In the above description, a combination of four shapes is used;and the same technique can be used for five or more core shapes.Generally, when the number of magnetic poles is 2 m and the number ofcore slots is 3 n (m and n are integers, n□4), a basic configuration ofa core shape is determined by setting its slot opening angles to anappropriate value ranging from 80° to 95° and from 20° to 35° inelectrical angle (from (80/m)° to (95/m)° and from (20/m)° to (35/m)° inmechanical angle). Furthermore, combining P core shapes each having theslots displaced by an angle equal to one-2P-th the cycle of basiccogging torque (180/(n·k))° in mechanical angle [k is a least commonmultiple of 2 m and 3 n]) allows a cycle of cogging torque to be reducedto one-2P-th the cycle of the basic cogging torque and its absolutevalue to be reduced considerably as well.

[0238] (Eleventh Embodiment)

[0239] Eleventh through eighteenth embodiments below will describetechniques of reducing cogging torque using core shapes which also varyin axial direction.

[0240]FIGS. 31A to 31C show core shapes in accordance with the eleventhembodiment.

[0241] In the eleventh embodiment, a case where the number of magnetpoles is “8” and the number of core slots is “6” is described as anexample. Since the number of the magnet poles is “8”, a mechanical angleof 90° corresponds to an electrical angle of 360°. The least commonmultiple of “8 and “6” is “24”; and thus the cycle of basic coggingtorque is 15° in mechanical angle, or 60° in electrical angle.

[0242] In FIGS. 31A through 31C, core 16 is configured so that openingangles of its salient pole tips are constant at 150° in electricalangle, and salient pole tip 4 in the upper half of the core is displaced1.875° (one-eighth the cycle of basic cogging torque) clockwise andsalient pole tip 4 in the lower half is displaced 1.875°counterclockwise. This core 16 is configured according to the followingidea.

[0243]FIG. 31B shows core 17 configured so that the opening angle ofslot 3 is set to 90° in electrical angle and salient pole tip 4 isdisplaced 1.875° (one-eighth the cycle of basic cogging torque)counterclockwise. For this core 17, salient pole tip 4 are configured ina manner slightly different from the basic configuration; however, asshown by the solid line in FIG. 32A, the core produces cogging torqueidentical to that produced by the basic configuration except that thephase is slightly different.

[0244]FIG. 31C shows core 18 configured so that the opening angle ofslot 3 is set to 90° in electrical angle and salient pole tip 4 isdisplaced 1.875° clockwise. Likewise, as shown by the solid line in FIG.32B, core 18 also produces cogging torque identical to that produced bythe basic configuration except that the phase is slightly different.

[0245] The cogging torque waveforms generated in these two cores 17 and18 are the same in absolute value and 180° out of phase (3.75° inmechanical angle, or one-quarter the cycle of the basic cogging torque).

[0246] Core 16 of the eleventh embodiment is configured by placing ahalf of core 17 shown in FIG. 31B on a half of core 18 shown in FIG.31C. As shown by the broken line in FIG. 32A, the upper half of core 17produces cogging torque having one-half the absolute value of and inphase with the cogging torque produced by the entire core 17 shown inFIG. 31B. The same holds true for the lower half of core 18. For core 16of the eleventh embodiment where these two halves are combined, coggingtorque waveforms generated by these halves cancel out each other, thuscanceling odd-numbered-order components of the cogging torque.Therefore, as shown in FIG. 32C, the resultant cogging torque has awaveform repeated 96 times per revolution and its cycle is one-half of(one-quarter the cycle of the basic cogging torque) and its absolutevalue is one-half or less than those generated by the basicconfiguration.

[0247] The above-mentioned structure reduces the cycle of cogging torqueto one-quarter or less the cycle of ordinary cogging torque as well asits absolute value. Therefore, the cogging torque can be reduced to theextent that its cycle is one-half of and its absolute value is one-halfor less than those produced with the conventional techniques describedin Japanese Patent Application Non-examined Publication No. H02-254954,Japanese Patent Application Non-examined Publication No. H03-3622, andothers.

[0248] Although the configuration of core 16 of the eleventh embodimentis similar to those in accordance with the techniques described inJapanese Patent Application Non-examined Publication No. H02-254954,etc., the angular displacement between upper and lower halves of core 16is one-half of that described in the above-mentioned publication. Thecore in accordance with the present invention is superior in reducingthe cogging torque to one-half or less while maintaining the efficiencyproduced by the basic configuration as much as possible.

[0249] (Twelfth Embodiment)

[0250]FIGS. 33A through 33C show core shapes in accordance with atwelfth embodiment. In this embodiment, like the eleventh embodimentmentioned above, a case where the number of magnet poles is “8” and thenumber of core slots is “6” is described as examples.

[0251] In FIG. 33A, core 16 is configured by placing laterally invertedtwo core halves one over the other. In each of the core halves, slotsare disposed with an equal angular pitch (60° in mechanical angle), andslots each having an opening angle of 18.75° (90° in electrical angle −one-quarter the cycle of basic cogging torque) and slots each having anopening angle of 26.25° (90° in electrical angle + one-quarter the cycleof the basic cogging torque) are alternately provided. This core shapeis more complicated than that of the eleventh embodiment; and, it isconfigured by combining two halves of cores 17 and 18 shown in FIGS. 34Aand 34B generating cogging torque waveforms 180° out of phase eachother.

[0252] The upper half of core 16 shown in FIG. 33B is configured by acombination of the diagonally shaded parts of cores 17 and 18 shown inFIGS. 34A and 34B, respectively. The lower half of core 16 is configuredby the parts other than the diagonally shaded parts of cores 17 and 18shown in FIGS. 34A and 34B. This shape has the same effects of reducingcogging torque that are produced by the above eleventh embodiment.Moreover, since core 16 is superior in vertical and lateral symmetry andmagnetic balance, its structure is advantageous to improve rotationalaccuracy.

[0253] (Thirteenth Embodiment)

[0254]FIGS. 35A through 35C show core shapes in accordance with athirteenth embodiment. In this embodiment, like the eleventh and twelfthembodiments mentioned above, a case where the number of magnet poles is“8” and the number of core slots is “6” is described as an example.

[0255] In FIG. 35A, core 16 is configured by placing vertically invertedtwo core halves one over the other. In each of the core halves, theopening angles of slots are constant at 90° in electrical angle, andslots each disposed with an angular pitch of 63.75° (a quotient of 360°divided by the number of slots + one-quarter the cycle of basic coggingtorque) and slots each disposed with an angular pitch of 56.25° (thequotient of 360° divided by the number of slots − one-quarter the cycleof the basic cogging torque) are alternately provided. This core is alsoa combination of the halves of cores 17 and 18 shown in FIGS. 36A and36B like the twelfth embodiment mentioned above.

[0256] The upper half of core 16 shown in FIG. 35B is configured by acombination of the diagonally shaded parts of cores 17 and 18 shown inFIGS. 36A and 36B, respectively. The lower half of core 16 shown in FIG.35C is configured by the parts other than the diagonally shaded parts ofcores 17 and 18 shown in FIGS. 36A and 36B. This shape has the sameeffects of reducing cogging torque that are produced by the eleventh andtwelfth embodiments described above. Moreover, since core 16 is superiorin vertical and lateral symmetry and magnetic balance like the twelfthembodiment, its structure is advantageous to improve rotationalaccuracy.

[0257] The configuration of core 16 of the thirteenth embodiment issimilar to those made by the techniques described in Japanese PatentApplication Non-examined Publication No. H03-3622, and others. However,in accordance with the description of these publications, cogging torquehas been reduced to only one-half the cycle of basic cogging torque. Inaccordance with the present invention, since predetermined relations areprovided between the slot opening angle and angular pitches in core 16,cogging torque is reduced to the extent that its cycle is one-half andits absolute value is one-half or less than those generated by theabove-mentioned techniques. Obviously, the present invention hastechnical advantages over those prior arts.

[0258] (Fourteenth Embodiment)

[0259]FIGS. 37A to 37C show core shapes in accordance with a fourteenthembodiment. Also in this embodiment, like the eleventh, twelfth, andthirteenth embodiments, a case where the number of magnet poles is “8”and the number of core slots is “6” is described as an example.

[0260] In FIG. 37A, core 16 is made of two core halves laterallyinverted each other. For the upper half of core 16, the salient poletips are disposed with an equal angular pitch (60° in mechanical angle),and the opening angles of salient pole tips 41 on a half side of theupper core are 33.75° (150° in electrical angle − one-quarter the cycleof basic cogging torque), and the opening angles of salient pole tips 42on the other side of the upper core are 41.25° (150° in electricalangle + one-quarter the cycle of the basic cogging torque). The lowerhalf of the core is configured by laterally inverting the upper half.Like the eleventh through thirteenth embodiments, this core shape isalso a combination of cores 17 and 18 shown in FIGS. 38A and 38B, thoughit may be rather complicated.

[0261] Unlike the cases described in the above twelfth and thirteenthembodiments, the shape of the fourteenth embodiment intends to unbalancethe lateral magnetic condition. This unbalanced condition adds momentforce of always attracting the magnet toward one direction, thusproviding an action for preventing the rotor from whirling with somedeviation. This shape is advantageous to improve rotational accuracywhen slide bearings such as an oil impregnated metal powder sinteredbearing are used as the bearing.

[0262] (Fifteenth Embodiment)

[0263]FIGS. 39A through 39C show core shapes in accordance with afifteenth embodiment. Also in this embodiment, like the eleventh throughfourteenth embodiments, a case where the number of magnet poles is “8”and the number of core slots is “6” is described as an example.

[0264] In FIG. 39A, core 16 is made by placing a core half over theother core half. In the upper half of core 16, slots are disposed withan equal angular pitch (60° in mechanical angle), and slots 31 on a halfside of the upper core have an opening angle of 18.75° (90° inelectrical angle − one-quarter the cycle of basic cogging torque) andslots 32 on the other half have an opening angle of 26.25° (90° inelectrical angle + one-quarter the cycle of the basic cogging torque).The lower half is configured by laterally inverting the upper half. Withintentionally unbalanced lateral magnetic condition like the elevenththrough fourteen embodiments mentioned above, this shape also has thesame effects that have been produced by the fourteenth embodiment.Furthermore, for the fifteenth embodiment, slots 32 having a largeropening angle disposed on one side serve as suitable spaces for placingposition sensitive elements such as Hall elements.

[0265] (Sixteenth Embodiment)

[0266] The sixteenth and seventeenth embodiments below will describe howto improve volumetric efficiency of a motor as well as its rotationalaccuracy by applying the same techniques.

[0267]FIGS. 41A through 41C show core shapes in accordance with thesixteenth embodiment. Also in this embodiment, like the eleventh throughfifteenth embodiments mentioned above, a case where the number of magnetpoles is “8” and the number of core slots is “6” is described as anexample.

[0268] While cores are made of upper and lower two halves in theeleventh through fifteenth embodiments, core 16 is configured bycombining upper, middle, and lower thirds.

[0269] The core shapes of upper and lower thirds are identical. In eachof these thirds, as shown in FIG. 41B, salient pole tips 4 are disposedwith an equal angular pitch, and salient pole tips have an opening angleof 33.75° (150° in electrical angle − one-quarter the cycle of basiccogging torque). In the middle third of the core as shown in FIG. 41C,salient pole tips 4 are disposed with an equal angular pitch, andsalient pole tips have an opening angle of 41.25° (150° in electricalangle + one-quarter the cycle of the basic cogging torque).

[0270] In addition to different opening angels of the salient pole tips,core 16 of the sixteenth embodiment is characterized in that the salientpole winding parts are narrower in the upper and lower thirds than themiddle third.

[0271] The core of the sixteenth embodiment is configured as follows.Each of the upper and lower thirds of core 16 is configured by combiningthe diagonally shaded parts of cores 17 and 18 shown in FIGS. 42A and42B, respectively. The middle third of core 16 shown in FIG. 41C isconfigured by the parts other than the diagonally shaded parts of cores17 and 18 shown in FIGS. 42A and 42B. This structure can considerablyreduce the cogging torque like the eleventh trough fifteenth embodimentsmentioned above.

[0272] In addition, for core 16 of the sixteenth embodiment, width W1 ofeach salient pole winding part in the upper and lower thirds is madesmaller than width W2 of each salient pole winding part in the middlethird, reflecting the difference in the opening angles of salient poletips. This is because there is no problem with magnetic properties inthe upper and lower thirds even though they have narrower winding parts.Since the opening angles of salient pole tips are smaller in the upperand lower thirds, the quantity of magnetic flux passing through thesalient pole winding parts thereof is smaller.

[0273] On the contrary, such narrower salient pole winding parts canproduce the following effects. FIG. 43A shows a cross section of asalient pole winding part of a core in accordance with the sixteenthembodiment; and FIG. 43B shows a cross section of a salient pole windingpart having a uniform width for comparison.

[0274] As shown in FIGS. 43A and 43B, insulation coatings 19 are appliedto the cores and coils 20 are wound thereon. As clearly understood bythe comparison of FIGS. 43A and 43B, the length of the coils per turn isshorter in the case shown in FIG. 43A. For this reason, when the bothcores are wound by the same coil, the coils shown in FIG. 43A have lowerresistance, thus producing higher volumetric efficiency of the motor. Inaddition, for this case, since the shape of wound coil 20 is hexagonal,the pressure applied to core edges is distributed at eight points.

[0275] Thus, even with thinner coating than shown in FIG. 43B, theequivalent insulating performance can be maintained, and volumetricefficiency of the motor can be improved by winding up more coils intothe space saved by the thinner insulation.

[0276] (Seventeenth Embodiment)

[0277]FIGS. 44A and 44B show core shapes in accordance with theseventeenth embodiment. In FIG. 44A, core 161 has three salient poles.The inner walls of the respective three salient poles are joined atlower part thereof by annular part 21. The upper core part having thethree respective salient poles is configured so that its salient poletips are disposed with an equal angular pitch, and the salient pole tipshave an opening angle of 33.75° (150° in electrical angle − one-quarterthe cycle of basic cogging torque). The lower core part is configured sothat its salient pole tips are disposed with an equal angular pitch, andthe salient pole tips have an opening angle of 41.25° (150° inelectrical angle + one-quarter the cycle of the basic cogging torque).

[0278] In FIG. 44B, core 162 is identical to core 161 in configuration,but vertically inverted. Combining respective annular parts 21 of cores161 and 162 together will make a core shape identical to that of theabove fourteenth embodiment, thereby providing a motor with minimizedcogging torque.

[0279] Moreover, winding coils on cores 161 and 162 with both coresseparated and assembling them thereafter allows coils to be wound on thearea where adjacent salient poles have hindered the winding inconventional structures. This substantially improves the space factor ofcoils, thus volumetric efficiency of the motor.

[0280] Thus, separating the core into several identical core parts makesit possible to substantially improve the motor characteristics whileminimizing a rise in manufacturing costs of cores.

[0281] In the above-mentioned case, the core shape in accordance withthe fourteenth embodiment has been separated into several parts.Similarly, the core shapes in accordance with the twelfth, thirteenth,fifteenth, and sixteenth embodiments can be separated into severalidentical core parts.

[0282] The above-mentioned eleven through seventeenth embodiments areexamples designed according to a basic configuration in which openingangles of core slots are set to 90° in mechanical angle. However, asdescribed in the first embodiment, it is preferable to set the openingangles of the slots of the basic configuration to an appropriate valueranging from 80° to 95° and from 20° to 35°. When the number of magnetpoles are set to 2 m (m is an integer), the above-mentioned preferablerange of slot opening angles can be expressed as from (80/m)° to (95/m)°and from (20/m)° to (35/m)° in mechanical angle. Each of theabove-mentioned embodiments having opening angles of core slots set to90° in electrical angle can be generalized by replacing 90° inelectrical angle with an appropriate value ranging from (80/m)° to(95/m)° and from (20/m)° to (35/m)° in mechanical angle.

[0283] Furthermore, the above-mentioned preferable range can begeneralized for the opening angles of salient pole tips. When a ratio ofthe number of magnet poles to the number of core slots is 4:3, for acore having salient pole tips whose opening angles are set to 150° inelectrical angle, the preferable range of salient pole tip to openingangles can be generalized by replacing 150° in electrical angle with anappropriate value ranging from (145/m)° to (160/m)° and from (205/m)° to(220/m)° in mechanical angle in a similar manner.

[0284] The above-mentioned eleventh through seventeenth embodiments aretypical examples of the core shapes in accordance of the presentinvention and other shapes can be used as well. In general, when thenumber of magnet poles is 2 m and the number of core slots is 3 n (m andn are integers), a basic configuration of a core shape producing coggingtorque having one-half the cycle of basic cogging torque is determinedby setting its slot opening angles to an appropriate value, ranging from80° to 95° and from 20° to 35° in electrical angle (from (80/m)° to(95/m)° and from (20/m)° to (35/m)° in mechanical angle). In addition,making coplanar and axial combinations of two shapes each having theslots displaced by an angle equal to one-quarter the cycle of the basiccogging torque ((90/k)° in mechanical angle [k is a least commonmultiple of 2 m and 6 n]) can provide a motor in which the coggingtorque has one-quarter the cycle of the basic cogging torque as well asa considerably reduced absolute value.

[0285] (Eighteenth Embodiment)

[0286] For the above-mentioned eleventh through seventeenth embodiments,one-quarter the cycle of basic cogging torque has been generated by acombination of two core shapes. In the following embodiments, techniquesof further reducing the cogging torque with a combination of four coreshapes will be described.

[0287] In the eighteenth embodiment, an example in which four coreshapes generating cogging torque waveforms 90° out of phase each otherare combined will be described.

[0288]FIG. 45A shows a core shape in accordance with the eighteenthembodiment.

[0289] Also in this embodiment, a case where the number of magnet polesis “8” and the number of core slots is “6” is described as an example.Since the number of magnet poles is “8”, a mechanical angle of 90°corresponds to an electrical angle of 360°. The least common multiple of“8” and “6” is “24”; and thus the cycle of basic cogging torque is 15°in mechanical angle, or 60° in electrical angle.

[0290] Four core shapes constituting core 22 of the eighteenthembodiment are shown in FIGS. 45B through 45E. Core 22 is configured bythese four core shapes 23, 24, 25 and 26 placed one on another so thatsalient pole tips of each core are 1.875° (one-eighth the cycle of thebasic cogging torque) displaced from each other.

[0291] This structure makes cogging torque waveforms generated byrespective cores 90° out of phase each other.

[0292] For the cogging torque waveform generated by core 22 that is acombination of the respective torque waveforms generated by these fourcore shapes, odd-numbered- and second-order components of respectivecogging torque waveforms are cancelled. Therefore, the cogging torque isreduced to an extent that its cycle is one-quarter the cycle of and itsabsolute value is much smaller than those generated by the cores of theeleventh through seventeenth embodiments.

[0293] (Nineteenth Embodiment)

[0294] In the eighteenth embodiment, an example of an axial combinationof the plane configurations of four cores has been described. Accordingto the idea of these eleventh through fifteenth embodiments, not onlyaxial but also coplanar combinations of core plane configurations can bemade.

[0295]FIGS. 46A through 46C show core shapes in accordance with anineteenth embodiment. Also in this embodiment, a case where the numberof magnetic poles is “8” and the number of core slots is “6” isdescribed as an example. In FIG. 46A, core 22 is configured byvertically combining two halves. The upper half has a planeconfiguration shown in FIG. 46B, and the lower half has a planeconfiguration shown in FIG. 46C.

[0296] Similar to the eighteenth embodiment, this core 22 is made of acombination of four shapes shown in FIGS. 47A through 47D generatingcogging torque waveforms 90° out of phase each other. In other words,the plane configuration shown in FIG. 46B is made by combining thediagonally shaded parts of cores 23 and 24 shown in FIGS. 47A and 47B;and the plane configuration shown in FIG. 46C is made by combining thediagonally shaded parts of cores 25 and 26 shown in FIGS. 47C and 47D.This structure can provide a motor generating extremely minimizedcogging torque with a combination of two instead of four core shapes,though making this structure is slightly complicated.

[0297] Furthermore, the plane configurations of the upper and lowerhalves of core 22 are laterally inverted. Therefore, since two corehalves are combined with one half inverted, only one type of core shapeis sufficient; and thus only one die is needed for manufacturing thecore. This allows motor characteristics to be improved while maintaininga rise in manufacturing costs.

[0298] According to the same idea, other core shapes can be produced.

[0299]FIGS. 48A through 48C show another example of a core shape inaccordance with the nineteenth embodiment. In FIG. 48A, core 22 isconfigured by vertically combining two halves. The upper half has aplane configuration shown in FIG. 48B, and the lower half has a planeconfiguration shown in FIG. 48C.

[0300] The plane configuration shown in FIG. 48B is made by combiningthe diagonally shaded parts of cores 23 and 24 shown in FIGS. 49A and49B; and the plane configuration shown in FIG. 48C is made by combiningthe diagonally shaded parts of cores 25 and 26 shown in FIGS. 49C and49D. With this structure, the same effects produced by the core shown inFIG. 46A can be expected.

[0301] The above-mentioned are typical examples; and similarly, varioustypes of other cores can be produced by making not only axial but alsocoplanar combinations of core plane configurations. Specificallydesigned combinations allow motor characteristics to be improved whileminimizing a rise in costs of manufacturing complicated core shapes.

[0302] While combinations of four core shapes have been described in theexamples of the eighteenth and nineteenth embodiments, the sametechniques can be used for three or more core shapes. In general, whenthe number of magnet poles is 2 m and the number of core slots is 3 m (mand n are integers), a basic configuration of a core shape is determinedby setting its slot opening angles to an appropriate value ranging from80° to 95° and from 20° to 35° in electrical angle (from (80/m)° to(95/m)° and from (20/m)° to (35/m)° in mechanical angle). In addition,combining j core shapes each having the slots displaced by an angleequal to one-2 j-th (° is an integer equal to 3 or more) the cycle ofbasic cogging torque ((180/(j·k)° in mechanical angle [k is a leastcommon multiple of 2 m and 6 n]) allows the cogging torque to haveone-sixth the cycle of the basic cogging torque and its absolute valueto be reduced considerably.

[0303] In the above descriptions of each embodiment, the methods ofmanufacturing cores have not been referred to specifically. Theabove-mentioned respective core shapes can be made relatively easily byprocessing a thin plate of magnetic material (e.g. silicon steel plate)with a press technique.

[0304] While cases where the magnetic field generating means is a magnethave been shown for each of these embodiments, the same effects can beexpected if other magnetic field generating means such as anelectromagnet or a rotor with interior magnet are used. Furthermore,while a magnet is outside and a core is inside for each embodimentmentioned above, the same effects can be expected when a magnet isinside and a core is outside. Moreover, while a magnet rotates withrespect to a core for each of these embodiments, the same effects can beexpected when a core rotates with respect to a fixed magnet.

[0305] For each of these embodiments, shown are cases in which theangular displacement of the slots in respective core shapes to becombined is one-quarter (one-sixth or one-eighth) the cycle of basiccogging torque. In order to maximize the effect of this invention, thedisplacement should strictly be set to the above-mentioned angle. Evenwhen the angle is not strictly set to the above-mentioned value for theconvenience of manufacturing, setting the value within ±10% allows thereduction of the second-order components of basic cogging torque by 70%;and whereby practical reduction of cogging torque can be accomplished,though its effect is smaller.

[0306] (Twentieth Embodiment)

[0307] For each embodiment mentioned above, only core shapes havecontributed to the reduction of cogging torque. In the twentiethembodiment, a method of further reducing cogging torque usingpolarization configurations together with the above-mentioned coreshapes will be described.

[0308] For the twentieth embodiment, the core shape of the secondembodiment will be described as an example. FIG. 50 is a schematicrepresentation showing polarized condition of magnet 2 in accordancewith the twentieth embodiment. As shown in FIG. 50, magnet 2 ispolarized so that poles are inclined a predetermined angle with respectto the center of magnet 2. FIG. 51A shows how cogging torque varies witha change in this angle of inclinations (hereinafter referred to as a“skew angle ”). FIG. 51B shows how motor efficiency varies with a changein skew angles.

[0309] As shown in FIG. 51A, cogging torque is minimized when skew angleβforms an angle of about 3.75° (one-quarter the cycle of the basiccogging torque) or 7.5° (one-half the cycle of the basic cogging torque)with respect to the center of the motor. This is because axiallyaveraged cogging torque is output to the motor axis by providing a skewangle equivalent to one (or two) cycle(s) of the cogging torque.

[0310] On the other hand, motor efficiency decreases as the skew angleis increased. Therefore, when it is desired to reduce cogging torque andmaintain motor efficiency at the same, the skew angle should be set to3.75° (one-quarter the cycle of the cogging torque); and when reductionof cogging torque is mainly desired, the skew angle should be set to7.5° (one-half the cycle of the cogging torque). Thus, a motor withextremely excellent characteristics can be provided.

[0311] For the twentieth embodiment, efficient cogging torque reductioneffects can be produced with a skew angle equal to or less than one-half(more preferably, one-quarter) the cycle of the basic cogging torquewithout affecting motor efficiency.

[0312] Actually, the angle at which cogging torque is minimized may varyby 10% or the like with variations in the axial lengths of the magnetand core. Generally, the skew angle should be set to 200/k° or less (kis a least common multiple of 2 m and 3 n) in central angle, morepreferably to (80/k)° to (100/k)°.

[0313] One of the conventional methods of providing a skew angle on amagnet in a similar manner is disclosed in Japanese Patent PublicationNo. 2588661. However, in the nineteenth embodiment of the presentinvention, efficient cogging torque reduction effects can be obtainedwith one-half or less the angle provided on the above-mentionedconventional magnet. The present invention also has excellent effects ofimproving motor characteristics while minimizing ill effects caused by alarger skew angle.

[0314] As described above, this invention can provide a motor generatingcogging torque having a short cycle and reduced absolute value. Inaddition, canceling different cogging torque waveforms in the same motorfurther shortens the cycle and considerably decreases the absolute valueof the cogging torque.

What is claimed is:
 1. A core for use in a motor, said motor including Nand S magnetic poles for generating a magnetic field to which said coreis opposed, said core comprising: a plurality of slots formed in saidcore, said slots have an electrical angle which is one of: a) between 80degrees and 95 degrees; and b) between 20 degrees and 35 degrees, anumber of said magnetic poles is 2 m and a number of said slots is 3 n(m and n are integers).
 2. A core for use in a motor, said motorincluding N and S magnetic poles for generating a magnetic field towhich said core is opposed, said core comprising: a plurality of slotsformed in said core, said slots have an electrical angle which is oneof: a) between 80 degrees and 95 degrees; and b) between 20 degrees and35 degrees wherein a first portion of said core is displaced from asecond portion of said core by an angle equal to ¼ of a basic coggingtorque cycle of said motor a number of said magnetic poles is 2 m and anumber of said slots is 6 n (m and n are integers).
 3. The core asdescribed in claim 2 wherein a ratio of said number of magnetic poles tosaid number of slots is 4:3, said core is configured so that openingangles of salient pole tips of said core are constant at electricalangle γ ranging from 145° to 160° ((γ/m)° in mechanical angle), and saidcore is configured so that the salient pole tips on a half side of saidcore are displaced clockwise by an angle equal to one-eighth the cycleof the basic cogging torque ((45/k)° in mechanical angle, where k is theleast common multiple of 2 m and 6 n), and the salient pole tips on theother half side are displaced counterclockwise by the same angle.
 4. Thecore as described in claim 2 wherein a ratio of said number of magneticpoles to said number of slots is 4:3, said core is configured so thatopening angles of salient pole tips of said core are constant at anelectrical angle δ ranging from 205° to 220° ((δ/m)° in mechanicalangle), and said core is configured so that the salient pole tips on ahalf side of said core are displaced clockwise by an angle equal toone-eighth the cycle of the basic cogging torque ((45/k)° in mechanicalangle, where k is the least common multiple of 2 m and 6 n), and thesalient pole tips on the other half side are displaced counterclockwiseby the same angle.
 5. The core as described in claim 2 wherein said coreis configured so that opening angles of slots of said core are constantat an electrical angle αranging from 80° to 95° ((α/m)° in mechanicalangle), and said core is configured so that the slots on a half side ofsaid core are displaced clockwise by an angle equal to one-eighth thecycle of the basic cogging torque ((45/k) in mechanical angle, where kis the least common multiple of 2 m and 6 n), and the slots on the otherhalf side are displaced counterclockwise by the same angle.
 6. The coreas described in claim 2 wherein said core is configured so that openingangles of slots of said core are constant at an electrical angle βranging from 20° to 35° ((β/m)° in mechanical angle), and said core isconfigured so that the slots on a half side of said core are displacedclockwise by an angle equal to one-eighth the cycle of the basic coggingtorque ((45/k)° in mechanical angle, where k is the least commonmultiple of 2 m and 6 n), and the slots on the other half side aredisplaced counterclockwise by the same angle.
 7. The core as describedin claim 2 wherein said core is configured so that slots of said coreare disposed with an equal angular pitch, and slots each having anopening angle equal to an electrical angle α (80° to 95°) − one-quarterthe cycle of the basic cogging torque ((α/m−90/k)° in mechanical angle,where k is the least common multiple of 2 m and 6 n) and slots eachhaving an opening angle equal to the electrical angle α (80° to 95°) +one-quarter the cycle of the basic cogging torque ((α/m+90/k)° inmechanical angle) are alternately provided.
 8. The core as described inclaim 2 wherein said core is configured so that slots of said core aredisposed with an equal angular pitch, and slots each having an openingangle equal to an electrical angle β (20° to 35°) − one-quarter thecycle of the basic cogging torque ((β/m−90/k)° in mechanical angle,where k is the least common multiple of 2 m and 6 n) and slots eachhaving an opening angle equal to the electrical angle β (20° to 35°) +one-quarter the cycle of the basic cogging torque ((β/m+90/k)° inmechanical angle) are alternately provided.
 9. The core as described inclaim 2 wherein a ratio of said number of magnetic poles to said numberof slots is 4:3, and said core is configured so that salient pole tipsof said core are disposed with an equal angular pitch, and salient poleseach having an opening angle equal to an electrical angle γ (145° to160°) − one-quarter the cycle of the basic cogging torque ((γ/m−90/k)°in mechanical angle, where k is the least common multiple of 2 m and 6n) and salient poles each having an opening angle equal to theelectrical angle γ (145° to 160°) + one-quarter the cycle of the basiccogging torque ((γ/m+90/k)° in mechanical angle) are alternatelyprovided.
 10. The core as described in claim 2 wherein a ratio of saidnumber of magnetic poles to said number of slots is 4:3, and said coreis configured so that salient pole tips of said core are disposed withan equal angular pitch, and salient poles each having an opening angleequal to an electrical angle δ (205° to 220°) − one-quarter the cycle ofthe basic cogging torque ((δ/m−90/k)° in mechanical angle, where k isthe least common multiple of 2 m and 6 n) and salient poles each havingan opening angle equal to the electrical angle δ (205° to 220°) +one-quarter the cycle of the basic cogging torque ((δ/m+90/k)° inmechanical angle) are alternately provided.
 11. The core as described inclaim 2 wherein a ratio said number of magnetic poles to said number ofslots is 4:3, and said core is configured so that salient pole tips ofsaid core are disposed with an equal angular pitch, and salient poles ona half side of said core have an opening angle equal to an electricalangle γ (145° to 160°) − one-quarter the cycle of the basic coggingtorque ((γ/m−90/k)° in mechanical angle, where k is the least commonmultiple of 2 m and 6 n) and salient poles on the other half have anopening angle equal to the electrical angle γ (145° to 160°) +one-quarter the cycle of the basic cogging torque ((γ/m+90/k)° inmechanical angle).
 12. The core as described in claim 2 wherein a ratioof said number of magnetic poles to said number of slots is 4:3, andsaid core is configured so that salient pole tips of said core aredisposed with an equal angular pitch, and salient poles on a half sideof said core have an opening angle equal to an electrical angle δ (205°to 220°) − one-quarter the cycle of the basic cogging torque((δ/m−90/k)° in mechanical angle, where k is the least common multipleof 2 m and 6 n) and salient poles on the other half have an openingangle equal to the electrical angle δ (205° to 220°) + one-quarter thecycle of the basic cogging torque ((δ/m+90/k)° in mechanical angle). 13.The core as described in claim 2 wherein said core is configured so thatslots of said core are disposed with an equal angular pitch, and slotson a half side of said core have an opening angle equal to an electricalangle α (80° to 95°) − one-quarter the cycle of the basic cogging torque((α/m−90/k)° in mechanical angle, where k is the least common multipleof 2 m and 6 n) and slots on the other half have an opening angle equalto the electrical angle α (80° to 95°) + one-quarter the cycle of thebasic cogging torque ((α/m+90/k)° in mechanical angle).
 14. The core asdescribed in claim 2 wherein said core is configured so that slots ofsaid core are disposed with an equal angular pitch, and slots on a halfside of said core have an opening angle equal to an electrical angle β(20° to 35°) − one-quarter the cycle of the basic cogging torque((β/m−90/k)° in mechanical angle, where k is the least common multipleof 2 m and 6 n) and slots on the other half have an opening angle equalto the electrical angle β (20° to 35°) + one-quarter the cycle of thebasic cogging torque ((β/m+90/k)° in mechanical angle).
 15. A core foruse in a motor, said motor including N and S magnetic poles forgenerating a magnetic field to which said core is opposed, said corecomprising: a plurality of slots formed in said core, said slots have anelectrical angle which is one of: a) between 80 degrees and 95 degrees;and b) between 20 degrees and 35 degrees wherein a first portion of saidcore is displaced from a second portion of said core by an angle equalto ⅙ of a basic cogging torque cycle of said motor a number of saidmagnetic poles is 2 m and a number of said slots is 3 n (m and n areintegers).
 16. A core for use in a motor, said motor including N and Smagnetic poles for generating a magnetic field to which said core isopposed, said core comprising: a plurality of slots formed in said core,said slots have an electrical angle which is one of: a) between 80degrees and 95 degrees; and b) between 20 degrees and 35 degrees anumber of said magnetic poles is 2 m and a number of said slot is 3 n (mand n are integers, m is greater than or equal to 4) wherein said coreis configured by combining P core shapes each having their respectiveslots displaced by an angle equal to one-2P-th the cycle of basiccogging torque ((180/n·k)° in mechanical angle, where k is a leastcommon multiple of 2 m and 3 n).
 17. A core for use in a motor, saidmotor including N and S magnetic poles for generating a magnetic fieldto which said core is opposed, said core comprising: a plurality ofslots formed in said core, said slots have an electrical angle which isone of: a) between 80 degrees and 95 degrees; and b) between 20 degreesand 35 degrees a number of said magnetic poles is 2 m and a number ofsaid slot is 3 n (m and n are integers) wherein said core is configuredby making coplanar and axial combinations of two core shapes each havingthe slots displaced by an angle equal to one-quarter the cycle of basiccogging torque ((90/k)° in mechanical angle, where k is a least commonmultiple of 2 m and 3 n).
 18. The core as described in claim 17 whereinsaid core has two different plane configurations in an axial direction,and is configured so that the opening angles of slots are constant at anelectrical angle α ranging from 80° to 95° ((α/m)° in mechanical angle),and salient pole tips in an upper half are displaced clockwise by anangle equal to one-eighth the cycle of the basic cogging torque ((45/k)°in mechanical angle, where k is the least common multiple of 2 m and 3n) and salient pole tips in a lower half are displaced counterclockwiseby the same angle.
 19. The core as described in claim 17 wherein saidcore has two different plane configurations in an axial direction, andis configured so that the opening angles of slots of said core areconstant at an electrical angle β ranging from 20° to 35° ((β/m)° inmechanical angle), and salient pole tips in a upper half are displacedclockwise by an angle equal to one-eighth the cycle of the basic coggingtorque ((45/k)° in mechanical angle, where k is the least commonmultiple of 2 m and 3 n) and salient pole tips in a lower half aredisplaced counterclockwise by the same angle.
 20. The core as describedin claim 17 wherein said core has two different plane configurations inan axial direction, an upper half of said core is configured so thatslots of said half are disposed with an equal angular pitch, and slotseach having an opening angle equal to an electrical angle α (80° to 95°)− one-quarter the cycle of the basic cogging torque ((α/m−90/k)° inmechanical angle, where k is the least common multiple of 2 m and 3 n)and slots each having an opening angle equal to the electrical angle α(85° to 95°) + one-quarter the cycle of the basic cogging torque((α/m+90/k)° in mechanical angle) are alternately provided, and a lowerhalf of said core is configured as a laterally inverted upper half. 21.The core as described in claim 17 wherein said core has two differentplane configurations in an axial direction, an upper half of said coreis configured so that slots of said half are disposed with an equalangular pitch, and slots each having an opening angle equal to anelectrical angle β (20° to 35°) − one-quarter the cycle of the basiccogging torque ((β/m−90/k)° in mechanical angle, where k is the leastcommon multiple of 2 m and 3 n) and slots each having an opening angleequal to the electrical angle β (25° to 35°) + one-quarter the cycle ofthe basic cogging torque ((β/m+90/k)° in mechanical angle) arealternately provided, and a lower half of said core is configured as alaterally inverted the upper half.
 22. The core as described in claim 17wherein said core has two different plane configurations in an axialdirection, an upper half of said core is configured so that openingangles of slots of said half are constant at an electrical angle αranging from 80° to 95° ((α/m)° in mechanical angle), and slots disposedwith an angular pitch equal to a quotient of 360° divided by the numberof the slots + one-quarter the cycle of the basic cogging torque((120/m+90/k)° in mechanical angle, where k is the least common multipleof 2 m and 3 n) and slots disposed with an angular pitch equal to thequotient of 360° divided by the number of the slots − one-quarter thecycle of the basic cogging torque ((120/m−90/k)° in mechanical angle,where k is the least common multiple of 2 m and 3 n) are alternatelyprovided, and the lower half of said core is configured as a verticallyinverted upper half.
 23. The core as described in claim 17 wherein saidcore has two different plane configurations in an axial direction, anupper half of said core is configured so that opening angles of slots ofsaid half are constant at an electrical angle β ranging from 20° to 35°((β/m)° in mechanical angle), and slots disposed with an angular pitchequal to a quotient of 360° divided by the number of the slots +one-quarter the cycle of the basic cogging torque ((120/m+90/k)° inmechanical angle, where k is the least common multiple of 2 m and 3 n)and slots disposed with an angular pitch equal to the quotient of 360°divided by the number of the slots − one-quarter the cycle of the basiccogging torque ((120/m−90/k)° in mechanical angle, where k is the leastcommon multiple of 2 m and 3 n) are alternately provided, and a lowerhalf of said core is configured as a vertically inverted upper half. 24.The core as described in claim 17 wherein a ratio of said number ofmagnetic poles to said number of slots is 4:3, said core has twodifferent plane configurations in an axial direction, an upper half ofsaid core is configured so that salient pole tips of said core aredisposed with an equal angular pitch, and salient poles on a half sideof said upper core half have an opening angle equal to an electricalangle γ (145° to 160°) − one-quarter the cycle of the basic coggingtorque ((γ/m−90/k)° in mechanical angle, where k is the least commonmultiple of 2 m and 3 n) and salient poles on the other half side havean opening angle equal to the electrical angle γ (145° to 160°) +one-quarter the cycle of the basic cogging torque ((γ/m+90/k)° inmechanical angle) and, a lower half of said core is configured as alaterally inverted upper half.
 25. The core as described in claim 17wherein a ratio of said number of magnetic poles to said number of slotsis 4:3, said core has two different plane configurations in an axialdirection, an upper half of said core is configured so that salient poletips of said core are disposed with an equal angular pitch, and salientpoles on a half side of said upper core half have an opening angle equalto an electrical angle δ (205° to 220°) − one-quarter the cycle of thebasic cogging torque ((δ/m−90/k)° in mechanical angle, where k is theleast common multiple of 2 m and 3 n) and salient poles on the otherhalf side have an opening angle equal to the electrical angle δ (205° to220°) + one-quarter the cycle of the basic cogging torque ((δ/m+90/k)°in mechanical angle) and, a lower half of said core is configured as alaterally inverted upper half.
 26. The core as described in claim 17wherein said core has two different plane configurations in an axialdirection, an upper half of said core is configured so that slots ofsaid core are disposed with an equal angular pitch, and slots on a halfside of the upper core half have an opening angle equal to an electricalangle α (80° to 95°) − one-quarter the cycle of the basic cogging torque((α/m−90/k)° in mechanical angle, where k is the least common multipleof 2 m and 3 n) and slots on the other half side have an opening angleequal to the electrical angle α (80° to 95°) + one-quarter the cycle ofthe basic cogging torque ((α/m+90/k)° in mechanical angle), and a lowerhalf of said core is configured as a laterally inverted upper half. 27.The core as described in claim 17 wherein said core has two differentplane configurations in an axial direction, an upper half of said coreis configured so that slots of said core are disposed with an equalangular pitch, and slots on a half side of the upper core half have anopening angle equal to an electrical angle β (20° to 35°) − one-quarterthe cycle of the basic cogging torque ((β/m−90/k)° in mechanical angle,where k is the least common multiple of 2 m and 3 n) and slots on theother half side have an opening angle equal to the electrical angle β(20° to 35°) + one-quarter the cycle of the basic cogging torque((β/m+90/k)° in mechanical angle), and a lower half of said core isconfigured as a laterally inverted upper half.
 28. A core for use in amotor, said motor including N and S magnetic poles for generating amagnetic field to which said core is opposed, said core comprising: aplurality of slots formed in said core, wherein said core is made ofupper, middle, and lower thirds and pole winding parts of said core aremade narrower in the upper and lower thirds than the middle third. 29.The core as described in claim 28 wherein in a case where a number ofmagnetic poles is 4 m and a number of core slots is 3 m (m is aninteger), core shapes of the upper and lower thirds are identical, andeach of these thirds is configured so that salient pole tips aredisposed at an equal angular pitch, and opening angles of said salientpole tips are set to an angle equal to an electrical angle γ (145° to160°) − one-quarter the cycle of basic cogging torque ((γ/m−90/k)° inmechanical angle, where k a the least common multiple of 2 m and 3 n),and a core shape of the middle third is configured so that salient poletips of said core are disposed at an equal angular pitch, and openingangles of said salient pole tips are set to an angle equal to theelectrical angle γ (145° to 160°) + one-quarter the cycle of the basiccogging torque ((γ/m+90/k)° in mechanical angle).
 30. The core asdescribed in claim 28 wherein in a case where a number of magnetic polesis 4 m and a number of core slots is 3 m (m is an integer), core shapesof the upper and lower thirds are identical, and each of these thirds isconfigured so that salient pole tips of said thirds are disposed at anequal angular pitch, and opening angles of said salient pole tips areset to an angle equal to an electrical angle δ (205° to 220°) −one-quarter the cycle of the basic cogging torque ((δ/m−90/k)° inmechanical angle, where k is a least common multiple of 2 m and 3 n),and a core shape of the middle third is configured so that salient poletips of said third are disposed with an equal angular pitch, and openingangles of said salient pole tips are set to an angle equal to theelectrical angle δ (205° to 220°) + one-quarter the cycle of the basiccogging torque ((δ/m+90/k)° in mechanical angle).
 31. The core asdescribed in claim 17 wherein said core is structured by combining aplurality of separated cores whose inner walls of a plurality of salientpoles are joined by an annular part.
 32. The core as described in claim28 wherein said core is structured by combining a plurality of separatedcores whose inner walls of a plurality of salient poles are joined by anannular part.
 33. The core as described in claim 31 wherein saidseparated cores are shaped identical.
 34. The core as described in claim32 wherein said separated cores are shaped identical.
 35. A core for usein a motor, said motor including N and S magnetic poles for generating amagnetic field to which said core is opposed, said core comprising: aplurality of slots formed in said core, said slots have an electricalangle which is one of: a) between 80 degrees and 95 degrees; and b)between 20 degrees and 35 degrees wherein a number of magnetic poles is2 m and a number of slots of said core is 3 n (m and n are integers),wherein said core is configured by combining j core shapes each havingtheir slots displaced by an angle equal to one-2 j-th (° is an integerequal to 3 or more) the cycle of basic cogging torque ((180/j·k)° inmechanical angle, where k is a least common multiple of 2 m and 3 n).36. The core as described in claim 2 wherein said core is structured bylaminating thin plates of magnetic material.
 37. The core as describedin claim 15 wherein said core is structured by laminating thin plates ofmagnetic material.
 38. The core as described in claim 16 wherein saidcore is structured by laminating thin plates of magnetic material. 39.The core as described in claim 17 wherein said core is structured bylaminating thin plates of magnetic material.
 40. The core as describedin claim 28 wherein said core is structured by laminating thin plates ofmagnetic material.
 41. The core as described in claim 35 wherein saidcore is structured by laminating thin plates of magnetic material.
 42. Amotor including: (a) magnetic field generating means having N and Smagnetic poles for generating a magnetic field; and (b) a core made ofmagnetic material and opposed to said magnetic field generating means;wherein one of said magnetic field generating means and said corerotates with respect to the other, wherein a number of said magneticpoles is 2 m and a number of slots of said core is 3 n (m and n areintegers), and a plurality of slots formed in said core, said slots havean electrical angle which is one of: a) between 80 degrees and 95degrees; and b) between 20 degrees and 35 degrees.
 43. A motorincluding: (a) magnetic field generating means having N and S magneticpoles for generating a magnetic field; and (b) a core made of magneticmaterial and opposed to said magnetic field generating means; whereinone of said magnetic field generating means and said core rotates withrespect to the other, wherein a number of said magnetic poles is 2 m anda number of slots of said core is 6 n (m and n are integers), aplurality of slots formed in said core, said slots have an electricalangle which is one of: a) between 80 degrees and 95 degrees; and b)between 20 degrees and 35 degrees wherein said core is configured bycombining two core shapes each having the slots displaced by an angleequal to one-quarter the cycle of basic cogging torque ((90/k)° inmechanical angle, where k is a least common multiple of 2 m and 6 n).44. A motor including: (a) magnetic field generating means having N andS magnetic poles for generating a magnetic field; and (b) a core made ofmagnetic material and opposed to said magnetic field generating means;wherein one of said magnetic field generating means and said corerotates with respect to the other, wherein a number of said magneticpoles is 2 m and a number of slots of said core is 3 n (m and n areintegers), a plurality of slots formed in said core, said slots have anelectrical angle which is one of: a) between 80 degrees and 95 degrees;and b) between 20 degrees and 35 degrees wherein said core is configuredby combining three core shapes each having the slots displaced by anangle equal to one-sixth the cycle of basic cogging torque ((60/k)° inmechanical angle, where k is a least common multiple of 2 m and 3 n).45. A motor including: (a) magnetic field generating means having N andS magnetic poles for generating a magnetic field; and (b) a core made ofmagnetic material and opposed to said magnetic field generating means;wherein one of said magnetic field generating means and said corerotates with respect to the other, wherein a number of said magneticpoles is 2 m and a number of slots of said core is 3 n (m and n areintegers, m≧24), a plurality of slots formed in said core, said slotshave an electrical angle which is one of: a) between 80 degrees and 95degrees; and b) between 20 degrees and 35 degrees wherein said core isconfigured by combining P core shapes each having the slots displaced byan angle equal to one-2P-th the cycle of basic cogging torque((180/n·k)° in mechanical angle, where k is a least common multiple of 2m and 3 n).
 46. A motor including: (a) magnetic field generating meanshaving N and S magnetic poles for generating a magnetic field; and (b) acore made of magnetic material and opposed to said magnetic fieldgenerating means; wherein one of said magnetic field generating meansand said core rotates with respect to the other, wherein a number ofsaid magnetic poles is 2 m and a number of slots of said core is 3 n (mand n are integers), a plurality of slots formed in said core, saidslots have an electrical angle which is one of: a) between 80 degreesand 95 degrees; and b) between 20 degrees and 35 degrees wherein saidcore is configured by making coplanar and axial combinations of two coreshapes each having the slots displaced by an angle equal to one-quarterthe cycle of basic cogging torque ((90/k)° in mechanical angle, where kis a least common multiple of 2 m and 3 n).
 47. A motor including: (a)magnetic field generating means having N and S magnetic poles forgenerating a magnetic field; and (b) a core made of magnetic materialand opposed to said magnetic field generating means; wherein one of saidmagnetic field generating means and said core rotates with respect tothe other, and wherein said core is made of upper, middle, and lowerthirds, and pole winding parts of said core are made narrower in theupper and lower thirds than the middle third.
 48. A motor including: (a)magnetic field generating means having N and S magnetic poles forgenerating a magnetic field; and (b) a core made of magnetic materialand opposed to said magnetic field generating means; wherein one of saidmagnetic field generating means and said core rotates with respect tothe other, wherein in a case where a number of said magnetic poles is 2m and a number of slots of said core is 3 n (m and n are integers), aplurality of slots formed in said core, said slots have an electricalangle which is one of: a) between 80 degrees and 95 degrees; and b)between 20 degrees and 35 degrees wherein said core is configured bycombining j core shapes each having the slots displaced by an angleequal to one-2 j-th (° is an integer equal to 3 or more) the cycle ofbasic cogging torque ((180/j·k)° in mechanical angle, where k is a leastcommon multiple of 2 m and 3 n).
 49. The motor described in claim 44wherein polarization is performed at a skew angle of (200/k)° or less incentral angle (k is the least common multiple of 2 m and 3 n).
 50. Themotor described in claim 45 wherein polarization is performed at a skewangle of (200/k)° or less in central angle (k is the least commonmultiple of 2 m and 3 n).
 51. The motor described in claim 46 whereinpolarization is performed at a skew angle of (200/k)° or less in centralangle (k is the least common multiple of 2 m and 3 n).
 52. The motordescribed in claim 47 wherein in a case where said magnetic fieldgenerating means is a magnet, and a number of magnet poles is 2 m and anumber of core slots is 3 n (m and n are integers), polarization isperformed at a skew angle of (200/k)° or less in central angle (k is aleast common multiple of 2 m and 3 n).
 53. The motor described in claim48 wherein polarization is performed at a skew angle of (200/k)° or lessin central angle (k is the least common multiple of 2 m and 3 n). 54.The motor described in claim 49 wherein polarization is performed at askew angle ranging from (80/k)° to (100/k)° in said central angle. 55.The motor described in claim 50 wherein polarization is performed at askew angle ranging from (80/k)° to (100/k)° in said central angle. 56.The motor described in claim 51 wherein polarization is performed at askew angle ranging from (80/k)° to (100/k)° in said central angle. 57.The motor described in claim 52 wherein polarization is performed at askew angle ranging from (80/k)° to (100/k)° in said central angle. 58.The motor described in claim 53 wherein polarization is performed at askew angle ranging from (80/k)° to (100/k)° in said central angle.